California’s arid Central Valley (CV) relies heavily on groundwater extracted from deep aquifers (>50 m) and imported surface water to sustain approximately one-quarter of the United States’ food production. While the recharge to deep aquifers in CV is hypothesized to be influenced by hydrologic processes in the adjacent Sierra Nevada, direct observational evidence at regional scales remains limited.</p> <p>Here, we present an integrated analysis of multi-decadal geodetic remote sensing, hydrologic, and climate datasets, including groundwater levels, GRACE-derived water storage, GNSS and InSAR deformation, and snowmelt observations, to investigate the spatiotemporal relationships between mountain hydrology and deep aquifer dynamics in the CV. A consistent sequence of seasonal signals emerges across independent datasets: peak groundwater levels in deep CV aquifers occur approximately one month after peak water availability from Sierra Nevada snowmelt, while peak groundwater storage inferred from GRACE lags groundwater levels by approximately three months.</p> <p>These phase delays indicate that groundwater systems respond to mountain hydrologic forcing through temporally distinct processes, with pressure signals propagating more rapidly than changes in bulk water storage. A simplified first-order diffusion analysis shows that the observed lag between snowmelt and the groundwater-level response is feasible, given plausible pressure propagation timescales in fractured mountain bedrock.</p> <p>Together, these results provide observational evidence consistent with a hydraulic connection between high-mountain aquifers and deep basin aquifers via mountain block recharge (MBR). Our findings highlight the importance of incorporating mountain-driven recharge processes and pressure dynamics into regional hydroclimate models and groundwater management strategies, particularly in snowmelt-dominated and water-stressed regions.